You start with 3 enemies per player in the staging area. We played a 3-player with just the standard core decks. It's a 4-stage and we never got past stage 2. I asked for a difficulty rating from the FFG staff and he gave it a 9. Definitely harder than Escape from Dol Guldur. We never even got to the Witch-King, who is separated from the main deck and enters play in Stage 4.
The Witch-King
Engagement: 40
Threat: 6
Attack: 6
Defense: 6
HitPoints: 11
Nazgul. Captain.
Players cannot play attachments on The Witch-King.
While The Witch-King is in the staging area, each character gets -1 Willpower.
Forced: After The Witch-King attacks, he returns to the staging area unless the defending player raises his threat by 3.
Rough.